This invention relates to the manufacture of toothed cutting blades, such as saw blades for band, hand or reciprocating saws, and blades for use in the surface modification technique described in U.S. Pat. No. 5,376,410 (MacKelvie).
Such blades are commonly formed by machining or punching tooth forms in the edge of a strip of suitable material such as tool steel, the resulting tooth forms then being subjected to finishing operations such as setting, hardening and sharpening. Tooth forms are selected according to the intended use of the blade. One characteristic which influences the cutting characteristics of the blade is the rake angle of the teeth. A positive rake angle favours aggressive cutting characteristics, while the planing characteristics desirable on the teeth of blades used in the technique of U.S. Pat. No. 5,376,410 call for a substantial positive rake angle together with control of surface penetration. Unfortunately, severely raked teeth formed by the conventional forming process tend to be structurally weak.
According to the present invention, a method of forming a toothed cutting blade comprises forming spaced slots in an edge of a blade preform to leave lands between leading and trailing walls defining the slots, at least the leading walls of the lands having a positive rake angle greater than that required in the finished blade, and the lands having aligned top surfaces between the slots, and then applying bending forces to at least selected lands such as to reduce the rake angle of their leading walls to a desired angle and to project their top surfaces adjacent the leading walls beyond said edge to form positively raked teeth with inclined back surfaces.
The slots in the edge of the blade preform may conveniently be produced by forming a row of apertures in a sheet of material, and cutting the sheet along a line intersecting the apertures in the row to leave a preform edge with slots of desired profile.